The invention relates to recuperators primarily for use in gas turbine engines, and more particularly to a fin construction for the header portions of such recuperators.
Plate-fin heat exchangers or recuperators have been used to pre-heat combustion-inlet air in a microturbine. A typical configuration for a heat exchanger includes a stacked array of cells of plate-fins, each cell including top and bottom plates, an internal finned member or matrix fin disposed between the plates, two external finned members on the outside surfaces of the cell, an inlet header finned member, and an outlet header finned member. The header finned members and matrix finned members are typically brazed or otherwise metallurgically bonded to the top and bottom plates. The inlet and outlet header finned members are also commonly referred to as crossflow headers because they are positioned at the inlet and outlet ends of the cell and because the flow of fluid through them is at an angle with respect to the flow of fluid through the matrix finned member.
In some applications, the pressure in the headers can reach high levels, which forces the top and bottom plates away from each other and creates tension in the header finned members. The header finned members thus perform a structural function as they tie the top and bottom plates together and resist deformation of the header portion of the cell that may be caused by the pressure in the cell. Accordingly, the header finned members must be sufficiently strong to resist such tensile deformation.
While the header finned members must perform the above-described structural function, the header finned members must also be constructed to not unduly restrict flow of air. The density of the fins must be selected to minimize the pressure drop through the headers. A balance must be found between maximizing header fin density to provide structural strength to the header, and minimizing header fin density to lower the pressure drop across the header.
One known method for balancing the structural and performance requirements of a header is to make the header wide enough to provide sufficient fin density to meet structural requirements while allowing enough flow area to meet pressure loss or performance requirements. To minimize the cost of tooling, standard header sizes have been implemented to cover a range of applications. Problems arise with these standard head sizes when volumetric constraints, non-typical operating conditions, or unusual performance specifications are required for a particular application.
The present invention seeks to balance structural and performance requirements in crossflow headers by presenting a graded approach to fin density. In this way, the present invention provides a higher density of fins in regions with the greatest structural demand while minimizing fin density where structural demands are lighter to minimize pressure loss.
More specifically, the present invention provides a recuperator or heat exchanger cell including top and bottom plates each including a manifold opening. The top and bottom plates are positioned relative to one another to align the respective manifold openings. The cell also includes a matrix finned member disposed between the top and bottom plates. The matrix finned member and the top and bottom plates together define matrix channels for the flow of fluid between the top and bottom plates in a first direction.
Also disposed between the top and bottom plates is at least one header finned member. The header finned member, together with the top and bottom plates, defines header channels for the flow of fluid between the top and bottom plates in a second direction at an angle to the first direction, and the header channels communicate between the matrix channels and the manifold openings. The header finned member includes a low fin density portion and a high fin density portion positioned between the low fin density portion and the manifold openings.
Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims, and drawings.